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May 9, 2013

Expanding agriculture in Amazon is ‘no-win’ scenario

Expanding agriculture into the Amazon rainforest could bring decreasing yields as climate feedbacks from deforestation reduce rainfall, according to scientists from the US and Brazil. Ultimately, clearing land to grow crops or pasture could become self-defeating.

“Agricultural expansion in Amazonia, beyond some limits, may be a no-win scenario,” Leydimere Oliveira of Brazil’s Federal University of Viçosa and Federal University of Pampa told environmentalresearchweb. “By expanding agriculture by an excessive amount, we lose important Amazon ecosystem services, such as carbon storage in the live rainforest and climate regulation. In the end, there are losses everywhere you look.”

Oliveira and colleagues from the Federal University of Viçosa, Federal University of Minas Gerais and Woods Hole Research Center, US, modelled forest carbon storage and soybean and pasture productivity in the Brazilian Legal Amazon in 2050 under different scenarios of deforestation and atmospheric carbon levels.

The addition of carbon dioxide to the atmosphere is likely to cause a decline in rainfall in eastern Amazonia, climate models indicate. The gas may also stimulate photosynthesis and cause plants to close down their stomata, increasing water-use efficiency.

Between 2004 and 2011, the rate of deforestation in Brazil declined but the country is under pressure to expand its agricultural production to meet domestic and global demand. With this in mind, the researchers looked at three land-use scenarios: a control scenario, using the 2002 deforestation map; the business-as-usual scenario, in which compliance with legislation is low and as much as 40% of forest inside protected areas is cut down by 2050; and the governance scenario, with extensive implementation of environmental laws and the expansion of protected areas.

The researchers used estimates of albedo and incoming surface radiation to calculate the precipitation anomaly after deforestation. This information helped estimate the productivity of the forest, soybeans or pasture.

“We used the simple linear-model approach because we wanted to test many future scenarios, so we needed a model that ran fast,” Oliveira told environmentalresearchweb.

Nearly every scenario, the team found, would see both carbon storage and agricultural yield decrease in Amazonia in the first half of the 21st century.

Under the governance scenario, for example, an increase in pasture area by 47% would be offset by a decrease of 24–30% in agricultural yield. As a result, pasture output would increase by only 3%. Similarly, if 10% of this additional pasture area was used for soybean, soybean output could actually decrease by 16%. In a business-as-usual scenario, with a 142% increase in Amazon agricultural area, pasture output could increase by 60% and soybean output could decrease by 26%.

“We expected to see some kind of compensation or off-put, but it was a surprise to us that high levels of deforestation could be a no-win scenario,” said Oliveira. “The loss of environmental services provided by the deforestation may not be offset by an increase in agriculture production.”

Previous studies did not account for the consequences of climate feedbacks from changes in land use, the researchers say.

The findings are particularly worrisome for eastern Pará and northern Maranhão, where local rainfall appears to depend strongly on forests, writes the team in Environmental Research Letters (ERL). Changes in land cover could potentially affect local climate to the point where agriculture becomes unviable. The researchers propose that agricultural expansion in Brazil should prioritize land already converted, and should be accompanied by comprehensive forest conservation.

Next, the team would like to use new models that account for non-linear interactions.